1. Field of the Invention
The invention relates to a receiver for television signals. Such a receiver may be, inter alia, a television receiver or monitor, a video recorder, or a compact disc video player. The invention particularly relates to a receiver for television signals, provided with a video memory of, for example, a field or picture memory for functions such as noise reduction, large-area flicker reduction or still picture, and further provided with an additional picture signal source for displaying, for example, teletext pages or On Screen Display information.
2. Description of the Art
A television receiver of the type described in the opening paragraph is known from U.S. Pat. No. 4,568,964. The additional picture signal source in this known receiver is a teletext decoder. This decoder generates a pixel signal which comprises the pixels of a teletext page to be displayed, as well as a predetermined value of a blanking signal for each pixel. The video memory includes a picture memory and comprises a matrix of memory elements in which samples of a picture signal to be displayed are stored in a predetermined manner. More particularly, a sample of the received video signal or a pixel of the teletext decoder is stored per memory element in the picture memory of the known receiver, dependent on the value of the blanking signal. To this end both the received video signal and the pixel signal of the teletext decoder are applied to a selector, in which selection is effected by means of the blanking signal. The signal thus selected is stored at the field frequency of the received video signal, for example, 50 Hz. In this known receiver the stored samples of the picture signal are subsequently read from the memory at the double field frequency, i.e. 100 Hz, and applied to a display screen. In the known receiver the usual large-area flicker is considerably reduced in this manner.
When the stored picture signal is displayed, the blanking signal blanks the video signal during the presence of a pixel of the teletext page. To this end the corresponding value of the blanking signal is also stored for each memory element in the picture memory, for example, by means of one extra bit per memory element.
In the known television receiver it is important that for each memory element both a video signal sample and a pixel of the teletext decoder are simultaneously applied to the selector, as well as the value of the blanking signal required for selection. In this respect it should be noted that the received video signal has a field frequency of 50 Hz, while the information for a teletext page to be displayed is obtained only once or sporadically. The teletext decoder in the known television receiver is therefore Provided with means, such as a teletext display memory and a fast character generator, for generating the pixel signal and the corresponding blanking signal also at a field frequency of 50 Hz. These means raise the costprice of such a television receiver.